In the design of lightweight structures, particular emphasis is placed on weight reduction. In this context, depending on the application, the lightweight structures shall meet different requirements concerning strength, fatigue tolerance and damage tolerance. In particular in aircraft engineering, a particular emphasis is placed on the damage-tolerance characteristics of lightweight structures.
The increase of the damage-tolerance characteristics can take place in various ways: the increase of the skin thickness, the use of additional local stiffening elements or the adaptation of the thickness of the skin to load requirements, etc. These methods only result in an increase of the weight of the lightweight structure. The use of materials with increased damage-tolerance characteristics, such as metal layer material or fiber-reinforced laminates, for instance, is another option.
Recently, metal-based-reinforced composite materials have increased in importance. Reinforcing metal materials with fibers makes it possible to clearly increase the mechanical characteristics and the damage tolerance characteristics of metal materials. However, usually, the improvement of material characteristics is very closely linked to significantly higher costs for composite materials. This is due to increased production costs.
The methods connected with the melting-on of base metal materials are very time-consuming and expensive. From among suitable manufacturing methods which are relatively economical, the bonding of metal sheets with fibers bound in adhesive foil has proven reliable.
From EP 0 312 151, a laminate is known which consists of at least two metal sheets, wherein a plastic layer is disposed between the sheets, which plastic layer is bonded to the metal sheets and includes glass filaments. Such metal laminates are in particular suitable for lightweight structures for aircraft-related applications because these structures have advantageous mechanical characteristics while being of low structural weight.
From EP 0 056 288 a further metal laminate is known, wherein polymer fibers from the group of aramides, polyaromatic hydracids and aromatic polyesters in a plastic layer are used. From EP 0 573 507 an alloy laminate material is known which comprises reinforcement fibers, embedded in a plastic matrix, which fibers being from a group consisting of carbon fibers, polyaromatic amide fibers, aluminum oxide fibers, silicon carbide fibers or mixtures thereof.
The advantages of laminated materials consist of clearly higher damage tolerance characteristics compared to equivalent monolithic sheets. The crack propagation characteristics of fiber-reinforced metal laminates are 10 to 20 times better than those of monolithic sheets.
However, when compared to those of monolithic materials, the static characteristics of known laminated materials are inferior. Depending on the adhesive systems and fiber types used, the limit of elasticity during exposure to tensile, compressive or shearing stress of known laminated materials is 5 to 20% below that of equivalent monolithic materials.